TypeAssert

Hack library for converting untyped data to typed data.

Warning for TypeAssert\matches_type_structure()

TypeStructure<T>, type_structure(), and ReflectionTypeAlias::getTypeStructures() are experimental features of HHVM, and not supported by Facebook or the HHVM team. This means that matches_type_structure() may need to be removed in a future release without warning.

We strongly recommend moving to TypeAssert\matches<T>() and TypeCoerce\match<T>() instead.

Installation

composer require hhvm/type-assert

Usage

TypeAssert provides functions that take a mixed input, and will either return it unmodified (but with type data) or throw an exception; for example:

<?hh // strict
use namespace Facebook\TypeAssert;
function needs_string(string $bar): void {
}

function main(): void {
  needs_string(TypeAssert\string('foo')); // type-safe and works fine
  needs_string(TypeAssert\string(123)); // type-safe, but throws
}

These include:

• string(mixed): string
• int(mixed): int
• float(mixed): float
• bool(mixed): bool
• resource(mixed): resource
• num(mixed): num
• arraykey(mixed): arraykey
• not_null<T>(?T): T
• instance_of<T>(classname<T>, mixed): T
• classname_of<T>(classname<T>, mixed): classname<T>
• matches<T>(mixed): T
• matches_type_structure<T>(TypeStructure<T>, mixed): T

Coercion

TypeAssert also contains the Facebook\TypeCoerce namespace, which includes a similar set of functions:

• string(mixed): string
• int(mixed): int
• float(mixed): float
• bool(mixed): bool
• resource(mixed): resource
• num(mixed): num
• arraykey(mixed): arraykey
• match<T>(mixed): T
• match_type_structure<T>(TypeStructure<T>, mixed): T

These will do 'safe' transformations, such as int-ish strings to int, ints to strings, arrays to vecs, arrays to dicts, and so on.

TypeSpec

You can also assert/coerce complex types (except for shapes and tuples) without a type_structure:

<?hh

use namespace Facebook\TypeSpec;

$spec = TypeSpec\dict(
  TypeSpec\string(),
  TypeSpec\int(),
);
$x = $spec->assertType(dict['foo' => 123]); // passes: $x is a dict<string, int>
$x = $spec->assertType(dict['foo' => '123']); // fails
$x = $spec->assertType(dict[123 => 456]); // fails
$x = $spec->assertType(dict[123 => 456]); // fails

$x = $spec->coerceType(dict[123 => '456']); // passes: $x is dict['123' => 456];

Shapes and tuples are not supported, as they can not be expressed generically.

matches_type_structure<T>(TypeStructure<T>, mixed): T

Asserts that a variable matches the given type structure; these can be arbitrary nested shapes. This is particular useful for dealing with JSON responses.

<?hh // strict

use namespace Facebook\TypeAssert;

class Foo {
  const type TAPIResponse = shape(
    'id' => int,
    'user' => string,
    'data' => shape(
      /* ... */
    ),
  );

  public static function getAPIResponse(): self::TAPIResponse {
    $json_string = file_get_contents('https://api.example.com');
    $array = json_decode($json_string, /* associative = */ true);
    return TypeAssert\matches_type_structure(
      type_structure(self::class, 'TAPIResponse'),
      $array,
    );
  }
}

You can use type_structure() to get a TypeStructure<T> for a type constant, or ReflectionTypeAlias::getTypeStructure() for top-level type aliases.

not_null<T>(?T): T

Throws if it's null, and refines the type otherwise - for example:

<?hh // strict
use namespace \Facebook\TypeAssert;

function needs_string(string $foo): void {}
function needs_int(int $bar): void {}

function main(?string $foo, ?int bar): void {
  needs_string(TypeAssert\not_null($foo)); // ?string => string
  needs_int(TypeAssert\not_null($bar)); // ?int => int
}

is_instance_of<T>(classname<T>, mixed): T

Asserts that the input is an object of the given type; for example:

<?hh
use namespace Facebook\TypeAssert;

class Foo {}

function needs_foo(Foo $foo): void {}

function main(mixed $foo): void {
  needs_foo(TypeAssert::is_instance_of(Foo::class, $foo));
}

main(new Foo());

is_classname_of<T>(classname<T>, mixed): classname<T>

Asserts that the input is the name of a child of the specified class, or implements the specified interface.

<?hh // strict
use namespace Facebook\TypeAssert;

class Foo {
  public static function doStuff(): void {}
}
class Bar extends Foo {
  <<__Override>>
  public static function doStuff(): void {
    // specialize here
  }
}

function needs_foo_class(classname<Foo> $foo): void {
  $foo::doStuff();
}

function main(mixed $class): void {
  needs_foo_class(TypeAssert::is_classname_of(Foo::class, $class));
}

main(Bar::class);

Credit

This library is a reimplementation of ideas from:

• @admdikramr
• @ahupp
• @dlreeves
• @periodic1236
• @schrockn

Security Issues

We use GitHub issues to track public bugs. Please ensure your description is clear and has sufficient instructions to be able to reproduce the issue.

Facebook has a bounty program for the safe disclosure of security bugs. In those cases, please go through the process outlined on that page and do not file a public issue.

License

Type-Assert is MIT-licensed.